Firefly self illuminating GTLS glow-rings and kit markers from sp2 - No battery required light sources for all possible applications. Powered by GTLS (Gaseous Tritium Light Sources) sourced from MB Microtec, the world leader in self illuminating products, the Firefly Kit Marker provides light continuosly for 10 years even during complete darkness.Suitable for operation between -60 degrees C and up to +80 degrees C, they will continue to work normally even when submersed under water.